(1) Field of the Invention
The present invention generally relates to an adaptive passive sonar signal processing method and system.
(2) Description of the Prior Art
Sonar signal processing systems are known in the art. Edelblute et al. U.S. Pat. No. 4,754,282 discloses a data analysis system which uses an Eckart filter that has weights that are updated in accordance with a beam formed output. However, this system does not consider the environmental factors existing in an ocean environment in which a target is located. Zurek et al. U.S. Pat. No. 4,956,867 discloses an adaptive noise canceling apparatus in which adaptive filtering is inhibited in certain circumstances. Dragoset, Jr. U.S. Pat. No. 5,448,531 discloses a method for adaptively creating a filter capable of removing coherent environment noise from a seismic recording. O""Brien, Jr. et al. U.S. Pat. No. 5,537,368 discloses an adaptive statistical filter system updated using data representative of sensed target motion and noise. Wynn U.S. Pat. No. 6,313,738 discloses an adaptive noise cancellation system that adaptively updates the weights of the system""s adaptive filters based upon an input signal.
Other prior art systems utilize Eckart filters whose coefficients are obtained using pre-defined spectral levels of the noise and target. However, sonar systems utilizing such Eckart filters typically detect signals and generate bearing, range, speed, aspect and depth information that has less than desirable performance, e.g., reliability and accuracy.
None of these aforementioned patents disclose the technique of using a filter having adaptively calculated coefficients that are based upon the power spectrum of the target and the total noise in the ocean environment in which the target is located.
It is therefore an object of the present invention to provide a sonar signal processing method and system that utilizes a filter that filters beamformed data based on received sonar signals emanating from a target or source in an ocean environment.
It is another object of the present invention to provide a sonar system that adaptively calculates filter coefficients that depend upon the gain of a sonar sensor array that receives the sonar signals.
Yet another object of the present invention is to provide a sonar system that system that adaptively calculates filter coefficients that depend upon the total noise in the ocean environment in which the target is located.
Thus, the present invention is directed to a method and system for processing received sonar signals. The method and system generate bearing data signals based on the received sonar signal. The method and system continuously determine the signal strength of the received sonar signal and also continuously determine the total noise from the received sonar signal in the ocean environment in which the target is located. The method and system provide a sensor gain in response to the determined total noise and the signal strength, and adaptively calculate filter coefficients from the sensor gain and the determined total noise. The method and system also filter the generated bearing data signals using a filter having the calculated filter coefficients. In one embodiment, an Eckart filter is used to filter the generated bearing data signals.
Additional objects, features, aspects and advantages of the present invention are apparent from the drawings and specification which follow.